Autumn is the time to think about preparing the ground for next season. Digging is best done in the autumn as it gives time for the soil to be broken down by frost. If you dig in spring and your soil is not fine enough for seed sowing you can add a layer of home made compost, or commercial peat free compost, over the surface to make a good seed bed.
Please note: we no longer advise double digging as it has been show to be totally unnecessary and to damage soil. See this page for raised beds started in a field that had not been cultivated for over 20 years.
If you are growing vegetables for the first time, on an old lawn or ground that has not been cultivated, then the ground will need to be dug. A lot of gardeners dig all of their plots, and apply large amounts of manure, every year. It is not always necessary to do either and some thought about what is to be grown will determine how a plot is prepared.
You will need to add some “organic matter” when you dig a bed for the first time. Organic gardeners will have a supply of home made compost available but if you are new to gardening you might not have a compost bin, start one as soon as you can! In place of garden compost you can use one of the many commercial composts available but if you want to be organic then you should avoid all peat based products. Look for the Soil Association symbol on the bag, it ensures that the material is organic.
Do not be tempted to fill the trench with compost and bury under soil as you need fine soil for seeds in the top couple of inches. Many organic gardeners spread organic matter on the soil after digging and leave it to overwinter. This is called ‘top dressing’ and helps to prevent damage to the soil structure due to compaction from heavy rain. It also gets the compost where is it most needed, in the top couple of inches. If you are starting in Spring you will need to knock down your newly dug soil and then rake in some compost. How much you use will depend on your soil, the recommendations given by the supplier and what you are going to grow in the bed.
Do not be tempted to dig in loads of manure or to spread lime on the bed as further treatment will depend on what you intend to grow. (Check the 4 course rotation article to find the correct soil treatment for particular crops.) The table below offers some suggestions for soil treatments but it really does depend on your soil and what has been there before. If the bed is in a old lawn and you have dug in the old turf, the soil should be relatively fertile.
|Crop||Suggested soil treatment|
|Potatoes, tomatoes, leeks||Apply manure in spring. DO NOT lime!|
|Summer cabbage, winter brassicas, spring cabbage, other brassicas||Apply compost in spring/summer.Apply lime if needed (check pH first)|
|Winter brassicas||Apply leaf mould|
|Winter tares (green manure)||Apply lime if needed (check pH first)|
|Root crops||Apply leaf mould in spring.|
If you want to make standard 4ft wide raised beds then you will need to edge the bed with timber or other suitable material. It is best to avoid pressure treated timber as the preservative used contains chemicals which could leech into the soil. Use any non-toxic preservative – not creosote! I have used
external emulsion paint with good results. The board should be 4″-6″ deep but you can use a higher surround if required. If you want to try to keep slugs out then fix some plastic guttering to the top of the board so that the curved face is away from the bed (see diagram). Coat the inside of the curve with cooking oil which needs to be renewed at regular intervals. The theory is that the slugs cannot get a grip and fall off.
Another advantage of using raised beds is that your bed will not need digging again for many years provided you follow the “no dig” guidelines and do not walk on the bed and protect it from heavy rain. If you restrict the width of the bed to 4ft it is easy to reach all parts without walking on the soil
so your feet do not compact the ground. Keeping the surface covered at all times by crops, compost or plastic sheeting, helps also prevent the soil from becoming compacted by heavy rain. These are standard organic growing techniques that help to produce healthy and productive soil, they are equally applicable to small and large beds.
© Colin Shaw, 1999. No part of this document may be reproduced in any form without the written permission of the author.